Multiband doublet antenna



July 18, 1961 D. p. TANG 2,993,206

MULTIBAND DOUBLET ANTENNA Filed Jan. 22, 1959 INVENTOR DOUGLAS D. TANG ATTORNEYS United States Patent 2,993,206 MULTIBAND DOUBLET ANTENNA Douglas D. Tang, Lindsay, Ontario, Canada, assign'or to Lindsay Antenna and Specialty Products Limited, Lmdsay, Ontario, Canada Filed Jan. 22, 1959, Ser. No. 788,422 Claims. (Cl. 343-814) This invention relates to a broad band antenna.

It is known that since the high V.H.F. band is approximately three times the frequency of the low V.H.F. band, then a dipole of length one-half wavelength at the centre of the low V.H.F. band will have a length three-halves wavelength at the centre of the high V.H.F. band. Such a dipole would, therefore, provide satisfactory reception on both bands, subject to'the split of the main lobe into side lobes (resulting in ghosts on the screen) during reception on the high V.H.F. band. It is known that the split of main lobe may be remedied by coupling in divers manners to the dipole described above, the second dipole of length one-half wavelength at the centre of the high V.H.F. band located less than a quarter wavelength from the first dipole and coupling them. In the United States Patent No. 2,697,130 which issued on October 12, 1954, to Yuen Tze Lo the two high band folded dipoles are connected in parallel to the downlead terminals of the low band dipole with reversal in polarity. In United States Patent No. 2,726,690, which issued on December 6, 1955, to R. S. Weiss, the shorter dipole is not connected to the downlead, but merely inductively coupled to the longer dipole.

The Weiss disclosure does not give a satisfactory pattern. The L0 patent does, but it is difficult and expensive to manufacture.

This invention results in a good pattern that can be manufactured cheaply.

This invention provides a longer member of folded dipole form of a length of slightly less than one-half wavelength at the mean low V.H.F. and three-halves wavelength at the mean high V.H.F. together with a shorter dipole antenna of length one-half wavelength to the mean high V.H.F. Although the longer member is similar in appearance to a folded dipole it differs electrically therefrom in that it is approximately centrally broken in both the folded dipole arms. The break in one of the arms of the longer member provides two terminals for connection to what would normally be the downlead terminals of the shorter wave length antenna while the break in the other of the arms of the longer member is connected to the antenna downlead. The longer member and the shorter dipole are substantially parallel and spaced for inductive coupling less than one-quarter wave length as in the prior art but the method of connection, placing the currents of the member and of the shorter antenna in series, as it does, provides for much better elimination of the side lobes than by the methods of the prior art. Moreover the connection of the shorter dipole to the longer member in this manner increases the effective length of the latter and it is found that the longer members need not be fully one-half wavelength to the mean low V.H.F. but only about 83% of this length. In a folded dipole type construction it will be understood that the considerable saving of material is thus achieved.

In the drawing which illustrates a preferred embodiment of the invention:

A mast 10 supports a cross boom 12 which mounts at its forward end the antenna element generally indicated at 14 and at its rearward end a reflector element 16 suitably spaced from element 14.

The antenna element comprises a longer antenna element 18 comprised of two U-shaped members arranged ice 2 to resemble the form of a folded dipole with the upper and lower arms 20 and 22 of the dipole vertically spaced from one another. The lower arm is broken for connection to the downleads 24 and the upper arm is broken for connection to leads 26.

A shorter folded dipole 28 of length one-half wavelength at the mean high V.H.F. (in North America about 28") is mounted on boom '12 parallel to element 18 and spaced therefrom a distance less than one-quarter wavelength at 216 megacycles. It will be appreciated that dipole 28 is formed from one continuous piece of tubing, the free ends of which connect with leads 26 as shown.

The dipole 28 and member 18 are preferably symmetrical about the same centre line of symmetry. The dipole 28 has its upper and lower arms 30 and 32 vertically disposed from one another and the upper arms 30 are centrally broken for connection to the leads 26, care being taken that the leads are connected in the right polarity so as to cancel rather than augment the side lobes.

This is achieved in the specific embodiment by connecting the right and left hand terminals of the upper arm 20 respectively to the right and left hand terminals of upper arm 30 while the terminals of lower arm 22 are connected to the downlead 24.

The connection of the shorter dipole 28 in this manner allows the shortening of the longer member 18 to about 83% of one-half wavelength at the mean low V.H.F. (in North America one-half wavelength at the mean low V.H.F. would be about 84") while member 18 need only be made about 70 from tip to tip, this resulting in a considerable saving of dipole material.

The antenna described herein has given excellent reception on both high and low bands and has demonstrated a satisfactorily low side lobe level on high band V.H.F. channels.

The dipole 28 need not be of the folded type.

There is, in effect, a dipole 28 tuned to resonate at a 'high frequency the take off of which includes the U- shaped members of the section 18, the whole being adapted to resonate at the low frequency and the dipole and the section 18 being closely spaced for inductive coupling.

I claim:

1. An antenna element for high and low band operation comprising a dipole, a second folded member having two parallel arms, said second member being parallel to said dipole and in close relation to said dipole, said second member being centrally broken in one of said arms and connected to the feed terminals of said dipole, and being centrally broken in the other of said arms for connection to the feed terminals of said antenna element, said second member having a span of approximately one-half wavelength at the mean frequency of the low band, said dipole having a span of about one-half wave length at the mean frequency of the high band, the polarity of the connections between said dipole and the said second member being such that the dipole acts to suppress the side lobes which would otherwise occur in reception of high band signals.

2. An antenna as claimed in claim 1 wherein the spacing of the dipole and the second member is less than one-quarter wavelength of the highest frequency in the high band.

3. An antenna element for high and low band operation comprising a dipole, a second folded member having two parallel arms, said second member being parallel to said dipole and in close relation to said dipole, said second member being centrally broken in one of said arms and connected to the feed terminals of said dipole, and being centrally broken in the other of said arms for connection to the feed terminals of said antenna element, the span of said second member being about 83% of one-half wave length at the mean frequency of the low band, said dipole having a span of about one-half wave length at the mean frequency of the high band, the polarity of the connections between said dipole and the said secondmember being such' that the dipole acts to suppress theside lobes which would otherwise occur in reception of high hand signals.

4. An antenna as claimed in claim 3 wherein the spacing of the dipole and the second member is less than onequarter wave length of the highest frequency in the high band. 7

5. An antenna as claimed in claim 3 wherein said di'- pole is of the folded type.

6. An antenna as claimed in claim 3 wherein the arms of said second member are vertically disposed from one another.

7. An antenna as claimed in claim 3 wherein the spacing in the dipole and second member is less than onequarter wavelength at the highest frequency in the high band and said second member and said dipoleare symmetrical about the centre line of symmetry.

8. An antenna as claimed in claim 1 wherein said dipole is of the folded type.

9. An antenna as claimed in claim 1 wherein the arms of said second member are vertically disposed from one another.

10. An antenna as claimed in claim 1 wherein said dipole is of the folded type with the arms forming said folded dipole vertically disposed from one another and wherein said feed terminals of said dipole are connected.

to the broken upper arm of said dipole, the arms of said second member being vertically disposed from one another, the broken lower arm of said second member being connected to said element feed terminals, the broken upper arm of said second member being connected to the feed terminals of said dipole as aforesaid and wherein the right hand and left hand terminals of said second member upper arm are connected to the right and left hand terminals of said dipole respectively.

References Cited in the file of this patent UNITED STATES PATENTS 2,045,987 Green June 30, 1936 2,283,914 Carter May 26, 1942 2,641,703 Valach June 9, 1953 

